Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, fatal dementia which has recently been shown to be transmissible from man to animals in the laboratory. CJD, like kuru, appears to be a slow-virus infection. The natural mode of transmission of CJD is unknown. A unique focus of CJD has been discovered among Libyan Jews in Israel. After a nation-wide study, the rate in Libyan Jews was about thirty times higher than in other groups living in that country. There were no familial cases. Preliminary studies suggested the possibility that CJD, perhaps like kuru, is acquired through ingestion of infected organs, specifically sheep brain. The proposed study is designed to examine this possibility. The study will also determine whether the agent responsible for CJD in Libyan Jews is unusually virulent or whether Libyan Jews are unusually susceptible.